The present invention relates to a braiding yarn made of expanded graphite for a gland packing which is to be used in a shaft seal part of a fluid apparatus or the like, and more particularly to a braiding yarn made of expanded graphite which can enhance the pressure resistance of a gland packing.
Conventionally, as a braiding yarn for a gland packing which is to be used in a shaft seal part of a fluid apparatus or the like, known is, for example, a braiding yarn 3 shown in FIG. 13. In the braiding yarn 3, a plurality of reinforcing fibers 2, 2 are embedded in the longitudinal direction with forming gaps in the width direction of an expanded graphite tape 1 of a predetermined width.
In the case where a plurality of braiding yarns are braided to obtain a gland packing, it may be requested to twist the braiding yarn 3 as shown in FIG. 14 in order to satisfactorily conduct the braiding.
However, the expanded graphite tape 1 is low in tensile strength and brittle, and edges of both end portions 1a, 1b in the width direction have low flaking resistance among expanded graphite particles. In edges of both end portions 1a, 1b in the width direction, namely, expanded graphite particles easily flake off In the case where the braiding yarn 3 of the inner-reinforce type is twisted to obtain a twisted braiding yarn 10 made of expanded graphite, moreover, large tensile and shearing forces act on the edges of both end portions 1a, 1b in the width direction, and hence cracks are formed with starting from the edges of both the end portions 1a, 1b in the width direction. Therefore, expanded graphite particles in and in the vicinity of the edges of both the end portions 1a, 1b in the width direction flake off.
When a plurality of braiding yarns 10 made of expanded graphite having a twisted structure are braided or twisted in a state where expanded graphite particles flake off in this way, flaking of expanded graphite particles is further advanced during the braiding or twisting process.
It is an object of the invention to provide a braiding yarn made of expanded graphite in which flaking of expanded graphite particles is reduced or prevented from occurring.
In order to attain the object, the braiding yarn made of expanded graphite according to the invention is characterized in that, in a braiding yarn made of expanded graphite which is to be used in a gland packing, the braiding yarn is twisted so that at least one end portion in a width direction of a braiding yarn base material in which reinforcing fibers are embedded in an expanded graphite tape is directed toward an inner side in the width direction of the braiding yarn base material. According to the invention, since a twisting process is performed so that at least one end portion in the width direction of a braiding yarn base material is directed toward the inner side in the width direction of the braiding yarn base material, large tensile and shearing forces do not directly act on the edges of the one end portion during a twisting process, and hence occurrence of cracks from the edges of the one end portion and flaking of expanded graphite particles due to the occurrence of cracks can be reduced.
The other braiding yarn made of expanded graphite according to the invention is characterized in that, in a braiding yarn made of expanded graphite which is to be used in a gland packing, the braiding yarn is twisted so that at least one end portion in a width direction of a braiding yarn base material in which reinforcing fibers are embedded in an expanded graphite tape is directed toward an inner side in the width direction of the braiding yarn base material and a portion between both end portions in the width direction is bent. According to the invention, in addition to the function that, during a twisting process, large tensile and shearing forces do not directly act on the edges of the one end portion and occurrence of cracks from the edges of the one end portion and flaking of expanded graphite particles due to the occurrence of cracks can be reduced, since the portion between both the end portions in the width direction of the braiding yarn base material is bent, the dimension in the width direction of the braiding yarn base material can be reduced, the twisting process is facilitated, and twisting workability can be improved.
The further braiding yarn made of expanded graphite according to the invention is characterized in that, in a braiding yarn made of expanded graphite which is to be used in a gland packing, a braiding yarn base material in which reinforcing fibers are embedded in an expanded graphite tape and part of expanded graphite particles on a side of a surface of the expanded graphite tape are removed by a blasting process and is twisted. According to the invention, part of expanded graphite particles which are on the side of the surface of the expanded graphite tape, and which are highly oriented at a high density where cracks easily occur are removed by the blasting process. During the twisting process, even when a large tensile force acts on the end portions in the width direction of the braiding yarn base material, therefore, occurrence of cracks from the end portions and flaking of expanded graphite particles due to the occurrence of cracks can be reduced.
The still further braiding yarn made of expanded graphite according to the invention is characterized in that, in a braiding yarn made of expanded graphite which is to be used in a gland packing, the braiding yarn is twisted so that at least one end portion in a width direction of a braiding yarn base material in which reinforcing fibers are embedded in an expanded graphite tape and part of expanded graphite particles on a side of a surface of the expanded graphite tape are removed by a blasting process and is directed toward an inner side in the width direction of the braiding yarn base material. According to the invention, in addition to the function that, during the twisting process, large tensile and shearing forces do not directly act on the edges of the one end portion and occurrence of cracks from the edges of the one end portion and flaking of expanded graphite particles due to the occurrence of cracks can be reduced, since part of the expanded graphite particles which are on the side of the surface of the expanded graphite tape, and which are highly oriented at a high density where cracks easily occur are removed by the blasting process, a function that, during the twisting process, even when a large tensile force acts on both end portions in the width direction of the braiding yarn base material, therefore, occurrence of cracks from the end portions and flaking of expanded graphite particles due to the occurrence of cracks can be reduced is added. Consequently, occurrence of cracks and flaking of expanded graphite particles due to the occurrence of cracks can be reduced more surely.
The still further braiding yarn made of expanded graphite according to the invention is characterized in that, in a braiding yarn made of expanded graphite which is to be used in a gland packing, the braiding yarn is twisted so that at least one end portion in a width direction of a braiding yarn base material in which reinforcing fibers are embedded in an expanded graphite tape and part of expanded graphite particles on a side of a surface of the expanded graphite tape are removed by a blasting process is directed toward an inner side in the width direction of the braiding yarn base material and a portion between both end portions in the width direction is bent. According to the invention, in addition to the function that, during the twisting process, large tensile and shearing forces do not directly act on the edges of the one end portion and occurrence of cracks from the edges of the one end portion and flaking of expanded graphite particles due to the occurrence of cracks can be reduced, since the portion between both end portions in the width direction is bent, the dimension in the width direction of the braiding yarn base material can be reduced, the twisting process is facilitated, and twisting workability can be improved.
The still further braiding yarn made of expanded graphite according to the invention is characterized in that, in a braiding yarn made of expanded graphite which is to be used in a gland packing, a braiding yarn base material in which reinforcing fibers are embedded in an expanded graphite tape and part of expanded graphite particles on a side of a surface of the expanded graphite tape are removed by a blasting process is twisted. According to the invention, since part of the expanded graphite particles which are on the side of the surface of the expanded graphite tape, and which are highly oriented at a high density where cracks easily occur are removed by the blasting process. During the twisting process, even when a large tensile force acts on the end portions in the width direction of the braiding yarn base material, therefore, occurrence of cracks from the end portions and flaking of expanded graphite particles due to the occurrence of cracks can be reduced. Consequently, occurrence of cracks and flaking of expanded graphite particles due to the occurrence of cracks can be prevented more surely.
The still further braiding yarn made of expanded graphite according to the invention is characterized in that, in the braiding yarn base material, the surface side of the expanded graphite tape on which the removal by the blasting process is performed is impregnated with a lubricating material. According to the invention, part of expanded graphite particles which are on the side of the surface of the expanded graphite tape, and which are highly oriented at a high density are removed by the blasting process, whereby gaps of high permeability are formed among the expanded graphite particles. Therefore, a lubricating material easily permeates through the gaps. When the gaps are impregnated with a lubricating material, it is possible to improve the lubricity, the adaptability, and the like of the braiding yarn made of expanded graphite.
The still further braiding yarn made of expanded graphite according to the invention is characterized in that the reinforcing fibers are embedded in the expanded graphite tape via an adhesive agent. According to the invention, high tensile strength of the reinforcing fibers is surely given to the braiding yarn made of expanded graphite by the adhesive strength of the adhesive agent, so that the tensile strength of the braiding yarn made of expanded graphite can be enhanced.
In each of the above-mentioned variants of the invention, xe2x80x9cso that at least one end portion in a width direction of a braiding yarn base material is directed toward an inner side in the width direction of the braiding yarn base materialxe2x80x9d means that, during the twisting process, one end portion only is directed toward the inner side in the width direction of the braiding yarn base material. For example, therefore, the one end portion may be previously bent toward the inner side in the width direction of the braiding yarn base material before the twisting process, and, during the twisting process, the one end portion may be caused to be directed toward the inner side in the width direction of the braiding yarn base material. Alternatively, the one end portion may be previously formed into a curled shape, a spiral shape, an obliquely inward-directed shape, or another shape, and, during the twisting process, the one end portion may be caused to be directed toward the inner side in the width direction of the braiding yarn base material.
The number of the braiding yarn base material is not restricted to one. A plurality of braiding yarn base materials may be stacked together, and the braiding yarn base materials may be twisted so that at least one end portion in a width direction of each of the braiding yarn base materials is directed toward an inner side in the width direction of the braiding yarn base material.
It is a matter of course that both end portions in a width direction of a braiding yarn base material may be directed toward an inner side in the width direction of the braiding yarn base material.
Furthermore, the terms that a portion between both end portions in the width direction of the braiding yarn base material is bent mean that, during the twisting process, a portion between both end portions in the width direction is requested only to be bent.